Components require heating for any number of reasons including stress relief, hardening and conditioning. Heat treatment may be global in that the whole component is heated or local in that a selected part of the component is heated.
Heat treatment on a global scale is usually performed using a furnace; this may take the form of a vacuum furnace, inert gas furnace or air furnace depending upon the application and the materials being processed. The furnace may use various types of heating source to raise the temperature of the component.
In the case of a vacuum furnace the transfer is predominantly by radiant heating. In this case the heat generated in the elements is released as infrared radiation, which is then absorbed by the component to raise its temperature.
In an inert gas furnace convection is the principal source of heat transfer. In this example the heat is transferred from the elements to a gas, which then heats the component by a process of conduction as it interacts with it in the furnace. As the gas cools upon contact with the component, it sinks in the furnace and is replaced by hotter gas.
Alternative heat treatment techniques use beds of powder fluidized using a high temperature gas, or baths containing a molten salt.
There are also various methods of localized heat treatment used extensively in industry. The difference between localized and global heat treatment is the requirement for only certain areas of the component to reach the heat treatment temperature while allowing other, temperature sensitive regions to be maintained at a lower temperature. The main methods used for applying local heat treatment are that of radiant heating, convective heating, induction heating and resistance heating.
Forced convection local heat treatment is also known and published in EP1734136 to the applicant. A cassette is placed around the portion to be treated using argon process gas which is heated and impacts upon the component to be heated as impingement jets. These high velocity jets produce high heat transfer due to their turbulent nature as they impact on the component. A feature of this system is that the process gas used to produce the impingement jets can be inert and used in conjunction with a gas atmosphere to facilitate the processing of reactive components such as titanium. The nozzles within the cassette can be configured to selectively supply hot gas or colder gas. Typically, the colder gas is supplied at the periphery of the cassette to inhibit heat spread from the localised treatment. The cassette has sealing means to inhibit the spread of heated gas from the cassette and an evacuation pipe removes used gas from the cassette to enable a continuous flow.
The forced convection system of EP1734136 is particularly suited for processing individual components and particularly localised sections of these components. There is a need, however, to provide a simplified system that enables simultaneous treatment of a number of different regions of components in order to reduce the cycle time required for processing an entire component.